Phase equilibria and thermodynamic evaluation of the Fe-Ti-V-O system in air

In this study, the iron-titanium-vanadium-oxygen (Fe-Ti-V-O) system in equilibrium with air was studied experimentally by high-temperature equilibration, quenching, scanning electron microscope and microprobe analysis coupled with critical assessment and thermodynamic evaluation. The properties of the liquid phase were successfully described with the quasichemical model by optimizing parameters only related to the Fe-Ti-O system; remaining parameters for the Fe-V-O and Ti-V-O sub-systems were adopted from recent optimisations. The model for the ruffle and hematite solid solutions were described with the compound energy formalism. The ferropseudobrookite solid solution was modelled with a simple polynomial model to include a small solubility V2O5. A final set of self-consistent thermodynamic parameters was estimated within acceptable error limits. Calculated isothermal projections at 1000 degrees C, 1100 degrees C, 1200 degrees C, 1300 degrees C, and 1400 degrees C of the Fe-Ti-V-O system in equilibrium with air are presented and compared to experimental observations.